Pneumatic fire alarm system



Jan. 28, 1964 w. B. BARNARD PNEUMATIC FIRE ALARM SYSTEM Filed Feb. 14, 1962 INVENTOR. MLLIAM B. .BARNARD ATTOE/VE Y United States Patent 3,119,368 PNEUMATIC FEE ALARM SYSTEM William B. Barnard, Pottstown, Pa., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Filed Feb. 14, 1962, Ser. No. 173,167 7 Claims. (Cl. 116102) It provides means for detecting leakage in the system, adequate alarm in the event of fire and supervision as to the condition of the pressure source. It is therefore an object of this invention to provide an improved self-contained pneumatic fire alarm system. Another object of this invention is to provide a system of this type with provision for maintaining a minimum drain on the pressure source during operation to provide for adequate periods of alarm. A further object of this invention is to provide a system of this type with provision for leakage detection and low pressure in the source. A still further object of this invention is to provide a simplified fire detection system requiring only a single pipe extending from the source to a plurality of zones to be protected. These and other objects of the invention will be apparent from a reading of the attached description and drawings wherein:

FIGURE 1 is a schematic diagram of the improved system,

FIGURE 2 is a sectional view of a detector used in the system, and

FEGURE 3 is a sectional view of one of the valves of the system.

My improved self-contained pneumatic alarm system as shown in FIGURE 1 utilizes a compressed air tank or bottle indicated at 10 as the source of fluid pressure for operation of the alarm and detecting apparatus. This type of pressure source permits the application of the pneumatic fire alarm system to installations where compressors and continuous energization equipment are not available. This simplifies the maintenance problem relative to a motor driven compressor or other suitable compressing equipment. The system herein does not utilize bleed air on standby operation and supervisory or monitor type control relative to the tank or source is provided to indicate the state of the source and to detect a pressure drop below necessary operating level.

The pneumatic source or tank 10 is connected through a hand valve 11 to a pipe line 12 and to a pressure reducing and regulating valve indicated generally at 14 which valve is conventional and utilizes downstream pressure from the valve portion of the regulator 15 through a conduit 16 back to the motive chamber indicated generally at 17. The pressure reducing valve herein supplies a normal low pressure to the system or an initial flow to the system as will be later described which is at a relatively low pressure. Associated with the pressure reducing valve is an orifice indicated generally at 20, this restriction being designed to limit .the actual flow through the pressure reducing valve in the event that the air is caused to flow therethrough. The pressure reducing valve 14 and Patented Jan. 28, 1964 ice restriction 20 establish a source of low pressure for the pneumatic fire alarm system which is connected through a single pipe line indicated generally at 25 to a plurality of detectors 27, 28 and 29 distributed throughout the space or zones to be protected or in which fire is to be sensed. These are zone detectors and the areas in which they are positioned will designate the zones in which the alarm is to be mounted in the event of fire. The single pipe line 25 simplifies the installation in that it requires only a single pipe from the source of air throughout the space to be controlled or sensed. Also positioned at the source location or adjacent the pressure reducing valve, assuming the same is to be positioned at or near the tank source 10, is a pressure responsive valve indicated generally at 35- having a mechanical latch 34. This valve is also schematically shown and it has its valve portion 36 connected to a pipe 37 leading directly to the tank 10 and around the pressure reducing valve 14 and restriction 20*. This in effect bypasses the pressure reducing valve and restriction and directly connects the tank to the pipe line 25. The pressure responsive valve 35 is normally closed and is operated by the pressure in the line 25 through a conduit 46 leading to a pressure responsive portion 41 of the valve or pressure chamber biased by a spring 38. With a reduction in pressure in the pipe line 25 which is sensed through the piping it} at the pressure chamber 41 of valve 35, it will open to directly connect the tank 10 to the pipe line 25 for purposes which will be later noted. As will be seen in FIGURE 3, the pressure responsive means includes the latch 34 which includes a pin 33 on the movable part of valve portion 36 cooperating with a movable spring bias detent 32 extending through the side of the valve to operate in a conventional manner. A directional check valve 39 included in this connection will prevent a reverse air flow to chamber 4-1 from line 25 when valve 36 is open. Thus it will provide a high pressure source around the pressure reducing valve 14 and restriction 20 and add a greater flow rate than would be provided through the restriction 20. Valve 35 includes the mechanical latch to lock it open once the pressure is reduced in the line 25. This insures full pressure for alarm.

While I have shown only three zone detectors, 27, 28 and 29, it will be understood that any number may be utilized and this will be determined basically by the size of the area or the number of zones which the system is to protect. Further, as will be later noted, each of the zone detectors may have a plurality of sensing elements associated therewith. The size of the source tank will be determined by the flow through the detectors 27, 28- and 29 since each simultaneously sounds an alarm in the event of fire in any zone. Thus, as will be seen in FIGURE 1, each zone detector is directly connected to the single pipe line 25 through a conduit or pipe such as is indicated by 47, 48 and 49. In addition, each detector has associated therewith an audible warning means or horns such as is indicated schematically at 50, 51 and 52 respectively. The zone detectors 27, 2S and 29 also have associated therewith thermal sensing elements indicated generally at 60 each element being a normally closed valve means con necting through a pipe line indicated at 61 from the single pipe line 25 to the portion of the detector to be later defined. In an individual zone, a plurality of thermal sensing elements or valves can be connected in parallel or bypass relationship with one another, such as is indicated in phantom at 62, and to detector 28. These thermal elements include a normally closed valve 63 such that the pipe or passage 61 from the pipe line 25 to the respective detector is normally closed to air flow by a latch 68 and opens on a rapid rise in ambient temperature surrounding the thermal element or bimetal 64 in the zone in which the detector is located. These units are shown in block in FIGURE 1 since they may talre many tor-ms and are shown generally in connection Wlih'illt; detector in FIGURE 2.

Thedetector shown-in section in FIGURE 2 is identical for all zones. It includes a casing member 65 having a piston or pressure responsive member 66 therein which divides the casing into two chambers identified at 70 and 71 respectively. The casing has a pair of inlets therein indicated generally at 73, 74 of which inlet 73 connects to the direct pipings 47, 48 or 4?. The inlet 74 connects to the thermal element 66 as indicated in the drawing. In addition, the casing has a pair of outlet passages 75, 76 connected respectively to the chambers 70, 71 which passages act as valve seats in the casing and cooperate with movable valve elements 77, 78 to isolate the passages 75, 76 from the chambers 70, 71 respectively. In the position shown in FIGURE 2 for the detector 27, the valve element formed by seat 75 and closure member 77 is normally closed and the piston 66 which operates the sameis positioned in its normal or de-energized location. This valve closes the passage from the pipe 25 through the piping 47, 48 or 49 to the chamber 76 of each detector and through the respective valve to the horn or audible warning device associated therewith. The piston 66 or pressure responsive means may be a diaphragm or any other movable member and is designed to position the valves as will be later described. It is biased in its normal position by means of a spring 78 which rests at one extremity against a battle 89 in the casing and bears against the piston. Its travel is limited by the engagement of the valve closure member 77 with the valve seat 75, the valve closure member being carried by the piston through a suitable shaft 82. Similarly the valve closure member 78 cooperating with the passage or valve seat 76 which includes a restriction 85 therein and operates as a vent to atmosphere is also carried by a shaft 36 mounted on or carried by the piston 66. The baffle 80 supporting the spring also serves as a guide for the shaft and hence the piston 66 within the casing 65. In addition, the piston carries a latch member 88 which cooperates with an adjustable latch pin 89 mounted in the casing to hold the piston in a predetermined position in which the valve formed by closure member 78 and seat 76 is engaged or closed.

As previously indicated, the thermal element 60 is a normally closed valve operated by a suitable thermal means responsive to a rapid rise in ambient temperature surrounding the element. Thus, as indicated in FIG- URE 2, the element includes the valve 63 which is biased by means of a spring 93 to an open position but is held in a closed position by means of a latch 63 engaging the end of the bimetal or thermal element 64. A suitable setting member 100 is included therewith to reset the thermal element 64 once it has responded to the rise in temperature and disengaged from the latch 68 allowing the spring 93 to open the valve 63 therethrough. As previously indicated, a number of thermal elements can be connected in a parallel piping connection or in a bypass piping connection between the single supply line or pipe 25 and a respective detector. Any one of such thermal elements responding to a rise in temperature will cause its associated valve to open allowing passage of air from the supply line or single pipe 25 to enter the chamber 71 of the respective detector.

It will be noted that the chamber 70 of the respective detectors is in direct communication with the pipe line 25 leading to the compressed air source 10 through the reducing valve 14 and restriction 20. Thus, the chamber and hence the piston 66 defining the same will have a low pressure present therein applying a force to the piston acting against the spring 78 therein. The spring is of suilicient magnitude such that the valve closing the passage 75 to the audible warning device or horn will be kept closed and hence no air can reach the horn to Operate the same. The chamber 71 on the other hand Will be communicating with atmosphere through the restriction in the passage or valve seat 76 but the line through the thermal element '60 to the pipe line or source line 25 will be normally closed. Under these circumstances no air should leak through the detectors in their standby position and hence no flow will be present through the restriction 20 and pressure regulating valve 14.

Upon a rise in temperature in any zone, the respective thermal element adjacent the same will respond to release its valve stem and hence valve closure member 63 opening the passage from the pipe line 25 to the chamber 71 which is vented to atmosphere. The restriction 85 is of larger dimension or cross-sectional area than the restriction 20 adjacent the regulating valve 14 and hence the air pressure in the line 25 will drop rapidly as air is vented through the chamber 71 from the pipe line 25. Although this pressure drop will occur in one detector only, the drop will be experienced throughout the line 25 and will also be present in the pressure chamber 41 of the pressure responsive valve 35. This drop in pressure will offset the force in the pressure chamber allowing the spring 33 associated therewith to open the valve 36 connecting the tank 14 with the high pressure directly to the line 25 and impressing a higher than the regulated pressure from valve 14 on the line 25. This sudden increase in pressure on line 25 will be felt by all detectors 27, 28 and 29 and will be applied respectively to the chambers 70 thereof to act against the pistons or pressure responsive means 66 therein. This force will be suflicient to overcome the restraint of the spring 78 in the detector allowing the piston and hence the shafts 82, 86 to move effecting a closure of the valve in the vent chamber 71 with seating of the valve closure member or plug 78 against the seat 76. At the same time, the valve controlling the flow from the chamber 70 to the audible warning device 50 for each detector in all of the zones will be opened, that is the valve closure member or plug 77 will move away from the valve seat 75 allowing air in the line 25 to sound all of the warning devices at the same time. The closure of the vented chamber 71 in the device operated by the rise in temperature associated With its thermal element or one of its thermal elements 60 will prevent further flow from the pipe line 25 through this vent chamber and since none of the other thermal elements are open at this time no further air can escape through the vented chambers of any of the detectors. The audible warning devices 54] will continue to sound indicating a fire until such time as the pressure in the source 10 drops to a level such that the air pressure therein cannot operate respective warning devices. It will be noted that as the respective pistons 66 in each of the detectors moves to the right or valve closure position for the vented chamber, the latch formed by latch 88 and pin 89 will become fixed, holding the respective valves open and closed as previously described. The associated manual reset member 89 with each detector must be operated to release the piston when the pressure in chamber 25 has been dropped before the piston will return to its normal position.

Also included in the line 25 is an additional pipe tap or pipe connection 162 connected into a pressure responsive switch means indicated at 104. This pressure responsive means is basically a diaphragm 165 operating against a spring 106 and with a contact means 107 operated upon movement of the diaphragm. The spring 106 is adjusted so that with pressures at and above the normal pressure set by the reducing valve 14, the contact means 107 will be open and the electrical circuit formed by conductors 168, 169 through the switch means 167 will not connect the electrical indicating means 110 or light to the source of power indicated at 112. With closure of the switch, the circuit is made through the conductors 168, 169 and the light 116 to the source of power energizing the same and indicating a low level of pressure on the line 25. This will indicate leaks in the system dropping the pressure therein somewhat below the regulated pressure set by reducing valve 14. At all pressures below this point the li ht 114) will be energized indicating leakage. However with operation of the thermal element the pressure in the line will drop below this point or whenever the source becomes exhausted the pressure in the line will drop below this point and the light bulb will be lighted. Thus, when the light 11% alone is lighted, and no warning device 59 is operated, a condition of leakage in the line is indicated. In addition to the pressure responsive means tea, a similar pressure responsive means 120 is connected through a pipe 121 to the tank It) ahead of the reducing valve. Its physical structure is identical with the device of 1M and is conventional in that it employs a diaphragm 125, a spring 126 and con tact means 127. The diaphragm provides with the casing of the switch a pressure chamber communicating directly with the tank and the spring 126 operates against the same to position the shaft operating the contact means 127. With normal pressure in the tank, the diaphragm is positioned such that the contact means 127 is open indicating that adequate pressure is provided at the tank sufficient for operating the warning system or alarm system. Whenever the apparatus begins to operate and the air flows from the tank through the pressure responsive valve 35 to the warning devices 5%), 51 and 52, air will be exhausted in the system and the pressure in the tank will drop. Prior to the time that the pressure is reduced to such a low level that the warning devices will no longer operate, the pressure responsive switch 120 will have its diaphragm moved under the influence of the spring 126 to a point where the contact mechanism 127 thereof will close. This will set up a circuit from the electrical source or conductors 112 through conductors 139, 131 to a second light 133 indicating an exhausted air supply.

Thus in operation, this self-contained pneumatic alarm system provides means for supplying pressure to the system, determining whether leaks exist in the system, and determining when the pressure supply has dropped to the point where it must be replaced. Operation of any of the thermal elements 60 associated with the detector will drop the pressure in the pipe line 25 leading out of the detector by allowing air to exhaust through the vented chamber '70 of the associated detector. This drop of pressure in the pipe line or supply line 25 below that fixed by the pressure reducing valve 14 and restriction 24) causes operation of the pressure responsive valve 35. Operation of the pressure responsive valve 35 connects the tank source in directly to the pipe line 25 raising the pressure therein and moving the piston 66 of the detectors to close the vented chambers 71 in each of the detectors, including the detector in which air is escaping and opening the respective valves leading to the audible warning devices or horns which are directly connected to the supply pipe 25. This operation will be continued until the pressure has dropped within the chambers 7&3 to a level where the respective warning devices or horns can no longer be operated. Prior to this time, however, the pressure responsive switch 128 will operate to energize the electrical indicating means 133 associated therewith indicating a loss of air supply. Leakage in the system without operation of any or" the thermal elements will be detected by the pressure responsive switch 164 which operates its associated contact mechanism to energize the associated indicating light 1143 indicating leakage in the system.

This apparatus provides a simplified alarm system which may be readily installed by the use of a single pipe from a self-contained bottle source to provide adequate sensing and warning throughout a plurality of zones. The simple pipe permits simplification in installation and the zone detectors connected thereto incorporate a single or plurality of thermal elements, depending upon the size of the zone.

In considering this invention it should be remembered that the present disclosure is intended to be illustrative only and the scope of the invention should be determined only by the appended claims.

I claim as my invention:

1. A pneumatic fire alarm system comprising, a source of compressed air, a plurality of zone detectors positioned in zones in which fire detection is desired, said zone detectors each including an audible warning means and a pressure responsive valve means for controlling the operation of said warning means, a single pipe line connected to all of said detectors and to said source of compressed air including a pipe means connecting said audible warning means and said valve means of the detector to said pipe line, a pressure reducing valve and a restriction included in said single pipe line near said compressed air source and establishing a predetermined low pressure in said line to each detector, a pressure responsive valve means connected to said source and said pipe line and adapted to bypass said pressure reducing valve and said restriction, said pressure responsive valve being responsive to a drop in pressure in said pipe line below said predetermined low pressure to open said pressure responsive valve and apply a higher than said predetermined low pressure to said pipe line and said detectors, a plurality of thermal elements connected to said detectors and responsive to a rapid rise in temperature in said zones, said thermal elements including valve means connecting said pipe line to a vented chamber of said detectors to drop the pressure in said pipe line and cause said pressure responsive valve means to be operated and bypass said pressure reducing valve to raise the pressure in said pipe line, the pressure responsive valve means in said detectors responding to the increase in pressure in said pipe line to operate said audible warning device and close the vented chamber of said detectors.

2. A pneumatic fire alarm system comprising, a source of compressed air, a plurality of zone detectors positioned in zones in which fire detection is desired, said zone detectors each including an audible warning means and a pressure responsive valve means for controlling the operation of said warning means, a single pipe line connected to all of said detectors and to said source of compressed air including means connecting said audible warning means and said valve means of the detector to said pipe line, a pressure reducing valve and a restriction included in said single pipe line near said compressed air source and establishing a predetermined low pressure in said line to each detector, a pressure responsive valve means connected to said source and said pipe line and adapted to bypass said pressure reducing valve and said restriction, said pressure responsive valve being responsive to a drop in pressure in said pipe line below said predetermined low pressure to open said pressure responsive valve and apply a higher than said predetermined low pressure to said pipe line and said detectors, a plurality of thermal elements connected to said detectors and responsive to a rapid rise in temperature in said zones, said thermal elements including valve means connecting said pipe line to a vented chamber of said detectors to drop the pressure in said pipe line and cause said pressure responsive valve means to be operated and bypass said pressure reducing valve to raise the pressure in said pipe line, the pressure responsive valve means in said detectors responding to the increase in pressure in said pipe line to operate said audible warning device and close the vented chamber of said detectors, and manual reset means positioned in said detector and operative to hold said pressure responsive valve means therein in said position operating said audible warning means and closing said vented chamber whenever the air pressure in said pipe line has reached a level to operate said pressure responsive valve means to this position.

3. A pneumatic fire alarm system comprising, a source of compressed air, a plurality of zone detectors positioned in zones in which fire detection is desired, said Zone detectors each including an audible warning means and a pressure responsive valve means for controlling the operation of said warning means, a single pipe line connected to all of said detectors andto said source of compressed air including means connecting said audible Warning means and said valve means of the detectors to said pipe line, a pressure reducing valve and a restriction included in said single pipe line near said compressed air source and establishing a predetermined low pressure in said line to each detector, a pressure responsive valve means connected to said source and said pipe line and adapted to bypass said pressure reducing valve and said restriction, said pressure responsive valve being responsive to a drop in pressure in said pipe line below said predetermined low pressure to open said pressure responsive valve and apply a higher than said predetermined low pressure to said pipe line and said detectors, a plurality of thermal elements connected to said detectors and re sponsive to a rapid rise in temperature in said zones, said thermal elements including valve means connecting said pipe lines to a vented chamber of said detectors to drop the pressure in said pipe line and cause said pressure responsive valve means to be operated and bypass said pressure reducing valve to raise the pressure in said pipe line, the pressure responsive valve means in said detectors responding to the increase in pressure in said pipe line to operate said audible warning device and close the vented chamber of said detector, and pneumatic electric alarm means connected to said source of compressed air ahead of said pressure reducing and pressure responsive valve means and operative to sound an alarm upon a decrease in pressure at said source beyond a predetermined level.

4. A pneumatic fire alarm system comprising, a source of compressed air, a plurality of zone detectors positioned in zones in which fire detection is desired, said zone detectors each including an audible warning means and a pressure responsive valve means for controlling the operation of said warning means, a single pipe line connected to all of said detectors and to said source of compressed air including means connecting said audible warning means and said valve means of the detector to said pipe line, a pressure reducing valve and a restriction included in said single pipe line in proximity with said compressed air source and establishing a predetermined low pressure in said line to each detector, a pressure responsive valve means connected to said source and said pipe line and adapted to bypass said pressure reducing valve and said restriction, said pressure responsive valve being responsive to a drop in pressure in said pipe line below said predetermined low pressure to open said pressure responsive valve and apply a higher then said predetermined low pressure to said pipe line and said detectors, a plurality of thermal elements connected to said detectors and responsive to a rapid rise in temperature in said zones, said thermal elements including valve means connecting said pipe line to a vented chamber or" said detectors to drop the pressure in said pipe line and cause said pressure responsive valve means to be operated and bypass said pressure reducing valve to raise the pressure in said pipe lines, the pressure responsive valve means in said detectors responding to the increase in pressure in said pipe line to operate said audible warning device and close the vented chamber of said detector, pneumatic electric alarm means connected to said source of compressed air ahead of said pressure reducing and pressure responsive valve means and operative to sound an alarm upon a decrease in pressure at said source beyond a predetermined level, and additional pneumatic electric alarm means connected to said pipe line downstream of said pressure reducing and pressure responsive valve means and responsive to a predetermined low pressure in said line below said regulated pressure and above the drop in pressure caused by operation of said thermal element to indicate a leak in said pipe line.

5. A pneumatic fire alarm system comprising, a selfcontained-source of compressed air, a plurality of zone detectors positioned in zones in which fire is to be detected, a single pipe line connected to all of said zone detectors and connected to said self-contained source of compressed air, said zone detectors each including an audible warning device and a pressure responsive means including valve means for connecting said audible warning means to said pipe line, means included in said pipe line for providing a regulated low pressure to each of said detectors with a given flow rate, additional means connected to said compressed air source and said pipe line responsive to a pressure therein below said regulated pressure to bypass said regulating means and connect said compressed air source direct to said pipe line, each of said zone detectors having a plurality of thermal elements associated therewith and operative to connect said pipe line to a vented chamber in said detector upon a rise in temperature in said zones above a predetermined level and thereby reduce the pressure in the pipe line below said regulated level, the pressure responsive means in said detectors responding to the high pressure of said source with operation of said first named pressure responsive means to effect connection of said warning means to said pipe line and close said vented chamber.

6. A pneumatic fire alarm system comprising, a selfcontained source of compressed air, a plurality of zone detectors positioned in zones in which fire is to be detected, a single pipe line connected to all of said zone detectors and connected to said self-contained source of compressed air, said zone detectors each including an audible warning device and a pressure responsive means including valve means for connecting said audible warning means to said pipe line, means included in said pipe line for providing a regulated low pressure to each of said detectors with a given flow rate, additional means connected to said compressed air source and said pipe line responsive to a pressure therein below said regulated pressure to bypass said regulating means and connect said compressed air source direct to said pipe line, each of said zone detectors having a plurality of thermal elements associated therewith and operative to connect said pipe line to a vented chamber in said detector upon a rise in temperature in said zones above a predetermined level and thereby reduce the pressure in the pipe line below said regulated level, the pressure responsive means in said detectors responding to the high pressure of said source with operation of said first named pressure responsive means to efiect connection of said warning means to said pipe line and close said vented chamber, all of said detectors becoming operative upon a rise in pressure with operation of said valve means to connect said source directly to said pipe line.

7. A pneumatic fire alarm system comprising, a selfcontained source of compressed air, a plurality of zone detectors positioned in zones in which fire is to be detected, a single pipe line connected to all of said zone derectors and connected to said self-contained source of compressed air, said zone detectors each including an audible warning device and a pressure responsive means in cluding valve means for connecting said audible warning means to said pipe line, means included in said pipe line for providing a regulated low pressure to each of said detectors with a given flow rate, additional means connected to said compressed air source and said pipe line responsive to a pressure therein below said regulated pressure to bypass said regulating means and connect said compressed air source direct to said pipe line, each of said zone detectors having a plurality of thermal elements associated therewith and operative to connect said pipe line to a vented chamber in said detector upon a rise in temperature in said zones above a predetermined level and thereby reduce the pressure in the pipe line below said regulated level, the pressure responsive means in said detectors responding to the high pressure of said source with operation of said first named pressure responsive means to eifect connection of said warning means to said pipe line and close said vented chamber, all of said detectors becoming operadevice is connected directly to said pipe line and said vented tive upon a rise in pressure with operation of said valve chamber is closed.

means to connect said source directly to said pipe line, References Cited in the file of this patent and manual reset means included in said detectors and operative to latch said pressure responsive means operat- 5 UNITED STATES PATENTS ing said valve detectors in a position where said Warning 3,014,206 St. Clair Slavin Dec. 19, 1961 

1. A PNEUMATIC FIRE ALARM SYSTEM COMPRISING, A SOURCE OF COMPRESSED AIR, A PLURALITY OF ZONE DETECTORS POSITIONED IN ZONES IN WHICH FIRE DETECTION IS DESIRED, SAID ZONE DETECTORS EACH INCLUDING AN AUDIBLE WARNING MEANS AND A PRESSURE RESPONSIVE VALVE MEANS FOR CONTROLLING THE OPERATION OF SAID WARNING MEANS, A SINGLE PIPE LINE CONNECTED TO ALL OF SAID DETECTORS AND TO SAID SOURCE OF COMPRESSED AIR INCLUDING A PIPE MEANS CONNECTING SAID AUDIBLE WARNING MEANS AND SAID VALVE MEANS OF THE DETECTOR TO SAID PIPE LINE, A PRESSURE REDUCING VALVE AND A RESTRICTION INCLUDED IN SAID SINGLE PIPE LINE NEAR SAID COMPRESSED AIR SOURCE AND ESTABLISHING A PREDETERMINED LOW PRESSURE IN SAID LINE TO EACH DETECTOR, A PRESSURE RESPONSIVE VALVE MEANS CONNECTED TO SAID SOURCE AND SAID PIPE LINE AND ADAPTED TO BYPASS SAID PRESSURE REDUCING VALVE AND SAID RESTRICTION, SAID PRESSURE RESPONSIVE VALVE BEING RESPONSIVE TO A DROP IN PRESSURE IN SAID PIPE LINE BELOW SAID PREDETERMINED LOW PRESSURE TO OPEN SAID PRESSURE RESPONSIVE VALVE AND APPLY A HIGHER THAN SAID PREDETERMINED LOW PRESSURE TO SAID PIPE LINE AND SAID DETECTORS, A PLURALITY OF THERMAL ELEMENTS CONNECTED TO SAID DETECTORS AND RESPONSIVE TO A RAPID RISE IN TEMPERATURE IN SAID ZONES, SAID THERMAL ELEMENTS INCLUDING VALVE MEANS CONNECTING SAID PIPE LINE TO A VENTED CHAMBER OF SAID DETECTORS TO DROP THE PRESSURE IN SAID PIPE LINE AND CAUSE SAID PRESSURE RESPONSIVE VALVE MEANS TO BE OPERATED AND BYPASS SAID PRESSURE REDUCING VALVE TO RAISE THE PRESSURE IN SAID PIPE LINE, THE PRESSURE RESPONSIVE VALVE MEANS IN SAID DETECTORS RESPONDING TO THE INCREASE IN PRESSURE IN SAID PIPE LINE TO OPERATE SAID AUDIBLE WARNING DEVICE AND CLOSE THE VENTED CHAMBER OF SAID DETECTORS. 